Atlas of Plant and Animal Histology
Plant tissues. Protection.

A) Organ: leaf, stoma.
Species: ( )
Technique: paraffin embedding, section stained with Alcian blue / safranin.

B) Organ: leaf, stoma.
Species: kiwi (Actinidia deliciosa).
Technique: paraffin embedding, section stained with Alcian blue / safranin.

C) Organ: leaf, stoma.
Species: pine (Pinus spp.).
Technique: vibratome section stained with Alcian blue / safranin.

Stomata are present in the aerial parts of the plants. They regulate gas and water exchange with the atmosphere. Stomata are composed of guard cells and a substomatal chamber, located under the guard cells. Stomata are scattered among epidermal cells, mostly at the same level as epidermal cells (image A), but they may also protrude (image B) or be somewhat sunken (image C). In the latter case, they can even be found in invaginations of the epidermis called stomatal crypts. Commonly, the guard cells are surrounded by a variable number of attached cells called subsidiary or companion cells. Guard and subsidiary cells are differentiated from epidermal cells by their morphology and size, as well as by the uneven thickening of their cell walls. Guard cells of the same stoma may be more or less separated, allowing an opening between them, known as pore or ostiole, which communicates the external environment with the substomatal chamber, and then with the internal tissues of the plant. Guard cells, subsidiary cells and substomatic chamber form the stomatal complex.


These micrographs were obtained with a scanning electron microscope from the surface of a kiwi leaf. Stomata are clearly visible among epidermal cells (A). Guard cells, depending on water content, may have their cell walls close to each another, closed stoma (B), or separated between each other, open stoma (C). (Images provided by Xurxo Mariño Gago. Dept. Plant Biology and Soil Sciences, Faculty of Biology, University of Vigo).

Updated: 2017-05-27. 12:52